The imprint of anthropogenic CO2 emissions on Atlantic bluefin tuna otoliths
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2016 Elsevier B.V. Otoliths of Atlantic bluefin tuna (Thunnus thynnus) collected from the Mediterranean Sea and North Atlantic Ocean were analyzed to evaluate changes in the seawater isotopic composition over time. We report an annual otolith 13C record that documents the magnitude of the 13C depletion in the Mediterranean Sea between 1989 and 2010. Atlantic bluefin tuna in our sample (n = 632) ranged from 1 to 22 years, and otolith material corresponding to the first year of life (back-calculated birth year) was used to reconstruct seawater isotopic composition. Otolith 18O remained relatively stable between 1989 and 2010, whereas a statistically significant decrease in 13C was detected across the time interval investigated, with a rate of decline of 0.05 yr-1 (-0.94 depletion throughout the recorded period). The depletion in otolith 13C over time was associated with the oceanic uptake of anthropogenically derived CO2..